i have removed a all the hair alge on my tank except for this one peice that has all kinds of small braches and is very pories and could not remove it. and thei water is fine and nitrates are down but i think because i couldnt remove the alge on the rock that it is seeding the tank. to the question i tock the rock out of the tank put it in a dark bag how long wil it tanke the for the alge on this rock to die thank for the help